© G
. Ber
ber
ich
Autonomous Underwater Vehicle (Atlas Sea Cat, Atlas Elektronik GmbH)
By the Sea Cat detected gas exhalations at the lake bottom
Why does the Size of the Laacher See Magma Chamber and its Caldera Size not go together? – New FindingsUlrich Schreiber & Gabriele Berberich
University of Duisburg-Essen, Essen, Germany
EGU General Assembly 2013 | Poster EGU2013-5908 | B444 | GMPV36/TS3.4 Corresponding author: [email protected] U (2009): Vulkane der Eifel. Spektrum Verlag Heidelberg.Holohan E, van Wyk de Vries B & Troll V. (2008): Analogue models of caldera collapse in strike-slip tectonic regimes. Bull. Volcanol., 70:773-796Acocella V, Funiciello R, Marotta E, Orsi G, and de Vita S. (2004): The role of extensional structures on experimental calderas and resurgence, J. Volcanol. Geotherm. Res., 129(1-3), 199-217.Roche O, Druitt TH, Merle O (2000): Experimental study of caldera formation. Journal of Geophysical Research, 105: 395Schmincke U (2000): Vulkanismus. Wissenschaftliche Buchgesellschaft, Darmstadt, pp. 264.
Loos J, Juch D & Ehrhardt W (1999): Äquidistanzen von Blattverschiebungen - neue Erkenntnisse zur Lagerstättenbearbeitung im Ruhrkarbon.– Zeit. f. angew. Geol., 45: 26 – 36.Ochmann N (1988): Tomografische Analyse der Krustenstruktur unter dem Laacher See Vulkan mit Hilfe von teleseismischen Laufzeitstudien. Mitt. Ing.- u. Hydrogeol. 30, pp. 108Viereck LG & v.d. Bogaard P (1986): Magma- und Wärmeinhalt der Magmakammer des Laacher Sees und des Riedener Vulkans. Forschungsbericht T86-174, Bundesministerium für Forschung und Technologie (BMFT), Karlsruhe, pp 1-98.Bahrig B (1985): Sedimentation und Diagense im Laacher Seebecken (Osteifel). Bochumer geol. geotechn. Arb. 19, pp 231v.d. Bogaard P & Schmincke HU (1984): The Eruptive Center of the Late Quarternary Laacher See Tephra. – Geol. Rundschau, 73: 933-980.v.d. Bogaard P (1983): Die Eruption des Laacher See Vulkans. Dissertation, Ruhr-Universität Bochum, 348 S.
Blo
ck b
ound
ing
faul
t
Thrust
Norm
al
Zone bounding fault
ConjugateStrike slip
Rotation
Marker
Voids
Source: Dibblee, 1977
a)
b)
c)
d)
R’-Shear plane
Development of scales & duplex structures
en-échelon R-Shear plane
Connection withP-Shear planes
Faults 2nd order
Position and conncention of Riedel shear planes along of a dextral strike-slip fault
(after Swanson 2006, J. Struct. Geol. 28, 456-473)
Our findings:
Erupted magma volume incl. bedrock: 0.5 km³
Bed rock
Bed
ro
ck
Bed
ro
ck
Dra
wn
by:
G. B
erb
eric
h
Pre-eruptive Szenario 1a (Schmincke 2009):
Magma chamberVolume: 18 km³ Width: 1kmDepth of top: 3 km
3 km
6.0 km³ eruptedMagma
Post-eruptive Szenario 1b (Schmincke 2009):
Erupted bed rock volume: 0.5 km³ Erupted magma volume: 6.0 km³ Total erupted volume: 6.5 km³
Magma chamberVolume: 18 km³ Width: 1kmDepth of caldera bottom: ~7 km
1 km
10.6 km
2.5 kmToday‘s caldera width
Bed
ro
ck
Bed
ro
ck
Pre-eruptive Szenario 2a(Schmincke 2009):
Magma chamberVolume: 18 km³ Width: 1.6 kmDepth of top: 3 km
Surface
1 km
18 k
m³
Mag
ma
cham
ber
vo
lum
e
12 k
m³
Mag
ma
cham
ber
vo
lum
e
Bed
ro
ck
Bed
ro
ck
3 kmBed rock
1.6 km
6.0 km³ eruptedMagma
Surface
18 k
m³
Mag
ma
cham
ber
vo
lum
e
Bed rock
Bed
ro
ck
Bed
ro
ck
0.5 km³erup. Magma
3 km
Bed rock
Surface
Bed
ro
ck
Bed
ro
ck
2.5 kmToday‘s caldera width
Debris of bed rock
Debris of bed rock
Bed
ro
ck
Surface
6 km
1.6 km
12 k
m³
Mag
ma
cham
ber
vo
lum
e
Post-eruptive Szenario 2b(Schmincke 2009):
Erupted bed rock volume: 0.5 km³ Erupted magma volume: 6.0 km³ Total erupted volume: 6.5 km³
Magma chamberVolume: 18 km³ Width: 1.6 kmDepth of caldera bottom: ~3 km
2.5 kmToday‘s caldera width
Debris of bed rock
>1 km³ ?
Mag
ma
cham
ber
volu
me
3.5 km
6.8 km
2.7 km
Munich
Hamburg
Amsterdam
Brussels
ViennaBudapest
Marseille
Rome
Bonn
Stockholm
Kopenhagen
WarsawBerlin
Prague
Genf
Ice border11 000 BP
ocooStooc
Turin
Stockholm
Turin
0 200 kmO
Genfnfnfnfff
TurinTurin
urg
rlinerlinrlin
urg
Beee
10
05
15
15
05
7065
0
502510
10
02
3011
16
03020605
0902
02
030505
05
1006
05
06
05
2 mm
5 mm
1 cm
5 cm1cm
5cm
10cm10cm
10cm
5 cm
1 cm
5 m
m
Gotland
Turin03
Total thickness of Laacher See ashes and tephra fans in Central Europe (after: van den Bogaard, 1983)
New EQ-Center of the last 40 years
Laacher See strike-slip fault (LSSSF)
Processed mining fieldExamples A and BMining exposureTectonic projectionProjection due to equidistances
of the large-scale strike-slip faults}
Analogue Models of Caldera Collapse in Strike-Slip Tectonic Regimes (from: Holohan et al. 2008)
Ruhr carboniferous: Equidistances of strike-slip faults (from: Loos et al. 1999)
10 m 8 m 4 m 2 m 1 m1,1 %/ 1,1 %
0,3 %/1,0%
0,13 Mio. ppb
0,10 Mio. ppb/0,21 Mio. ppb
0,16 Mio. ppb/0,22 Mio. ppb
0,7 Mio. ppb
0,8 Mio. ppb
0,23 Mio. ppb
0,16 Mio. ppb/ 0,21 Mio. ppb
0,16 Mio. ppb
0,30 Mio. ppb
0,17 Mio. ppb/0,11 Mio. ppb
0,38 Mio. ppb
0,16 Mio. ppb0,18 Mio. ppb/0,46 Mio. ppb
Strike-slip faults and crustal block rotation with voids (after: Dibblee, 1977; Swanson 2006)
a) Pre-caldera strike-slip deformation
Outline of magmachamber at depth
Y-shearChamber-localised
graben and fault
Regional faults (Riedel shears)
b) Early downsag phase
Diffuse zone of peripheral
extension
Elliptical downsag zone inside
chamber outline
c) Initiation of reverse faulting
Reverse fault scarp forms a short axis end of chamber
Focus of asymmetry is initially to the NW
Component of horizontal movement during early
central zone subsidence
d) Final caldera structure Reverse fault propagates toward chamber long axis
Regional fault reactivated
Regional fault reactivatedto accomodate peripheral extension and/or central
subsidence
Second reverse fault forms.Central zone subsidence
becomes less asymmetric and purely vertical
e) Interpretation
Subsidence controlling
reverse fault
Zone of diffusive peripheral extension
Peripheral extension
localised on reactivated pre-existing
fault
Subsidence controlling
reverse faultReactivated Riedel shear
Pre-collapse regional faults(Riedel shears)
Pre-collapse faults(unreactivated)
f) Excavation of remnant chamber
Subsided, almost flat, upper surface of remnant chamber
Ridge bends sharply into
Y-shear trend. Displacement transfer from reverse fault to Y-Shear?
Cut into chamber made by regional R- and Y-shears. Associated with arrest of reverse fault propagation
Ridge with parallel outward dipping furrow
Vertical ridge. Inward dipping at SW end
Scale 10 cm
Scale 10 cm
Scale 10 cm
Scale 10 cm
Scale 10 cm
Scale 10 cmN
N
N
N
N
N
Under pressure experiments of Roche et al. (2000)
Platewithhole
Sandpack
Silicone
Tube
a) Apparatus, section view
Smalldeep chamber
Breccias
Roof
Chamber
Chamber
RoofLargeshallow chamber
Breccias Breccias
c) Final model summarizing the deformation pattern for funnel (small deep chamber) and piston (large shallow chambers) calderas (modified after Roche et al. 2000)
San
d-p
ack
Silicone
San
d-p
ack
SiliconeS
and
-pac
k
b) Section view of 3 experiments characterized by very different aspect ratios of the chamber roof
Silicone
Schematic models of Laacher See magma chamber sizes and erupted volumes
Sea Cat tracks of 2010 and 2011 campaigns
Profile of Laacher See (reflection seismic; Bahrig 1985)
Break-up zone below Laacher See (Ochmann 1988)
2010
2011
Sonar image of rising gas bubbles from Laacher See bottom (300 kHz side scan sonar)
New model concepts on the tectonic evolution of the young East Eifel lead to a contradiction in terms of size of the postulated magma chamber and the Laacher See Caldera
Due to the slow movement rates of active tectonic faults (mm per year), an estimated 18 km³ magma chamber beneath the Laacher See (v. d. Bogaard & Schmincke 1984) cannot be
confirmed. Discrepancies are given by
• the volume of the Laacher See caldera of approx. 0.5 km³ with regard to the pre-eruptive surface (Viereck & v.d. Bogaard 1986) and the erupted volume of 6.3 km³ dry rock equiva-
lent of lava and bed rock (v. d. Bogaard & Schmincke 1984) resp. 6.5 km³ magma (Schmincke 2009),
• a comparison of modeling of caldera evolution with the Laacher See Caldera formation (Holohan, de Wries & Troll 2008; Acocella, Funiciello, Marotta, Orsi & de Vita 2004),
• no geophysical prove of such a large magma chamber,
• a volume compensation of approx. 6 km³ by ascending magma from the mantle which could have prevented a further subsidence of the magma chamber
(over a period of several days of the estimated duration of eruption) appears unrealistic,
• performed sonar recordings of the post-eruptive Laacher See sediment layers (Bahrig 1985) that do not show any displacements that might indicate a doming caused by magma.
Our findings
• No statistical significant data set with regard to spatial distribution of the erupted tephra volume, e.g. only one sample point for North Italy (v.d. Bogaard 1983).
• Overestimation of the tephra thickness in published isopach maps of the Westerwald and other regions.
• More critical evaluation of interpretations of tephra samplings from old maps and literature is required.
• Inclusion of atmospheric effects (e.g. atmospheric turbulences, dune formation, dust storms long after the eruption, congestion of air masses at the alpine orogene) is required.
• An order of magnitude smaller magma chamber stretched over a longer vertical crustal section can help to better match the given tectonic movement rates and
the size of the caldera.
• All sampling locations would also be explained by an erupted volume of only 10% of the estimated one by Schmincke (2009).
© J
. Kal
wa,
AT
LAS
Ele
ktro
nik
Gm
bH
© J
. Kal
wa,
AT
LAS
Ele
ktro
nik
Gm
bH
© J
. Kal
wa,
AT
LAS
Ele
ktro
nik
Gm
bH
© J
. Kal
wa,
AT
LAS
Ele
ktro
nik
Gm
bH
Pre-existing fault reactivated to accomodate
peripheral extension
Reverse fault truncates
against regional fault